Sumo is as ancient as it is quintessentially Japanese. Historians agree that the sport dates back at least 2,000 years, and in its current form has remained largely unchanged since the Edo period.
Rigid in its ceremony, the actual bouts often last mere seconds, and much of the time the two opponents face off in the "dohyo" -- a raised clay dais -- is spent going through a set of ritualized traditions. Settling down on their haunches, the two "rikishi" -- wrestlers -- face off before standing again, walking to their respective corners and their seconds, before throwing salt into the ring to purify it.
While viewing figures have declined in the last two decades, watching the sport -- televised or otherwise -- during the six yearly grand tournaments, or "honbasho," is a uniquely Japanese experience that fans hope will never fade away. Euan McKirdy/CNN
Each year sees six grand tournaments, or "honbasho," that last for 15 days each, and the top-ranked wrestlers will contest one bout each day.
The final tournament of the year, in the city of Fukuoka on the southern island of Kyushu, is one of the biggest annual events in the region. JIJI PRESS/AFP/AFP/Getty Images
In recent years there has been considerable hand-wringing about the state of the sport, with a paucity of Japanese wrestlers making the top grade.
Recently, a "yokozuna," or grand champion, a Mongolian who wrestled under the nom de guerre of Asashoryu, turned many fans off with his snarling, aggressive displays, often rank with gamesmanship and, traditionalists thought, disrespectful of the sport. More recently, however, his countryman, a stellar yokozuna by the name of Hakuho (pictured), who earlier in 2015 broke the all-time tournament win record, clinching his 33rd trophy in the January honbasho, has been an exemplar of the solemnity and ceremony of this form-filled martial art, and has brought fans back into the fold. TOSHIFUMI KITAMURA/AFP/AFP/Getty Images
The spiritual home of the sport is the Ryogoku Kokugikan in Sumida Ward, Tokyo. It hosts the Spring, Summer and Autumn tournaments. The original Kokugikan was built in the early 20th century, as the sport gained popularity in Meiji-era Japan.
Now the sport needs to compete with Japan's other two major spectator sports, baseball and soccer. While there are sumo clubs for all ages, and a competitive varsity-level league, interest in the sport, which requires intense dedication and levels of privation that many young Japanese are not willing to endure, is waning and the top echelons of the sport dominated by overseas wrestlers. Chris McGrath/Getty Images AsiaPac/Getty Images
The area around the Kokugikan is rife with sumo memorabilia and themed restaurants. Alongside the Edo-Tokyo museum, the stadium is one of the main draws for fans.
The sport is becoming more internationalized -- the three yokozuna are all Mongolian, and a Bulgarian, who wrestled under the nom de guerre Kotooshu, was the first European to win the Emperor's Cup.
Japan and Mongolia's wrestling traditions share a lot in common, and as a result there have been more wrestlers from the landlocked Asian nation entering the ranks. Euan McKirdy/CNN
"Japanese people aren't as interested in sumo as they used to be," one woman told CNN in Mizuguchi, a shokudo (Japanese home-style cooking) restaurant in the Asakusa neighborhood. A big flat screen TV dominates one wall, and the owner is known for her rich knowledge of the sport.
The customer, who asked that CNN not use her name, said: "Like most sports in Japan, it's becoming more international. The Japanese (wrestlers) aren't hungry. The Mongolians are hungry." Euan McKirdy/CNN
During the out-of-town tournaments, Ryogoku is quiet but especially during the three annual Tokyo Grand Tournaments, the place thrums with a unique mix of culture and tradition, with rikishi an ever-present sight in the neighborhood.
Reminders of the neighborhood's association with the sport, like this small statue in the west entrance of Ryogoku station, are everywhere. Euan McKirdy/CNN
Unsurprisingly, sumo wrestlers have to eat vast amounts. One of their staples is the incredibly protein-rich chanko nabe, a hot pot made up of broth, various meats and vegetables. Restaurants in Yokoami, the neighborhood where the Kokugikan is located, specialize in the dish.Three middle-aged "salarymen," Yasunobu Nasu, Tsuyoshi Watanabe and Minoru Maki, of the Japan Frozen Noodle Association, Nisshin Flour Milling and Shimada Corp., a noodle manufacturer, are eating in Kirishima, a local chanko restaurant, four floors up and overlooking the station and keep half an eye on the bouts that regularly spring to life on the big-screen TV mounted prominently on one wall of the restaurant. They agree that the Japanese rikishi are getting weaker -- indeed, there is only one Japanese wrestler in the yokozuna and ozeki -- the second tier -- ranks.
"That's ok, though," Nasu says. "Maybe this will help raise the popularity of our sport outside Japan." Euan McKirdy/CNN
Retiree Masahiko Sawada, pictured here with his wife Reiko, is a huge fan who watches the honbasho tournaments regularly, setting his daily schedule during the bimonthly, two-week-long events around the later bouts, which start around 5 p.m. each day and where the higher-ranked wrestlers, like his personal favorites Teranouchi and Tochioza, take to the dohyo.
Despite his interest in the sport, however, he confesses that he has never been to watch a honbasho live. He says the concept of "yamato damashi" -- the unique Japanese spirit, sometimes fancifully translated as "samurai soul" is waning in Japan.
He says that the influx of foreign rikishi, however, isn't a problem. "Asashoryu was a strong, powerful wrestler," he says. "But he lacked class. Hakuho is different. He's very calm, more 'Japanese.'" Euan McKirdy/CNN
This small dohyo, in a faceless park in a faceless suburb of Tokyo, is an increasing rarity in the capital -- or for that matter, almost anywhere in Japan. The neighborhood committee voted to build the clay structure in the park here because they wanted to promote a sport that teaches kids respect.
They practice three times a week, even as winter approaches and they stand, steaming breath and feeling the sweat chill on their torsos. There are also two girls in this stable, sisters who train with and spar against the boys. One of the girls recently won a regional tournament. Euan McKirdy/CNN
Aubrey Sato, the mother of two of the smaller boys in the group, Yuki and Masato, says her two boys have just started training at the neighborhood dohyo.
She says her sons were the ones who made the decision to start training. She says she's not worried about them getting injured ("Injuries, some scratches. It's part of the training. So they will get tough and strong") as the experience of learning and training in the sport will be beneficial to their development.
"By practicing sumo it's about what you can get by training your heart and your body as well," she says. "Through training I think it's great that they get to train their heart and body at the same time." Euan McKirdy/CNN
When CNN visited on an uncharacteristically warm, rainy early November evening there were around six boys, ranging in age from 14 down to seven or eight.
The eldest two, middle schoolers, Ryota Sato and Wataru Nihonyanagi, have filled out and look the part, but the younger boys still are slight -- the ribs of youngest, Masato, still stick out as he goes through the drills and practice bouts with his stablemates and the instructor, Koichi Sakuma.
Wataru says he got into the sport when an elderly neighbor remarked that he was a big kid and suggested trying the sport out, where he might have an advantage, not necessarily evident in modern imports like baseball or soccer. He's been training since he was seven -- he's now 14 -- and says the sport has taught him "courtesy and has improved the training of my mind." Euan McKirdy/CNN
Ryota, the oldest of the six, says that his friends and classmates aren't surprised that he's chosen this sport, "because I'm quite big." Even though the training is grueling and requires a great commitment, he says he's never even thought about quitting.
Both he and Watauru want to be rikishi when they're older. Wataru's hero is the former Japanese great Chiyonofuji, who had a career record of 807 victories, while Ryota prefers the now-retired bad boy Asashoryu.
"I like him because he's cool," he says. Ryota echoes his stablemate when he pays tribute to the mental aspect of training. "It's more than just the training of the body," he says. "It's about discipline, respect and becoming a better person.
"Also, once when it was snowing, my neighbor asked me to help push his two-ton truck." Euan McKirdy/CNN
During the day coach Koichi Sakuma works in a convenience store. He has been training kids for 30 years.
"Becoming a yokozuna is equivalent to becoming a divine figure, so it's really important for (sumo wrestlers) to maintain and preserve Japanese tradition.
"There's a saying in Japanese martial arts: 'everything begins with politeness and ends with politeness.' This dohyo actually began with a suggestion from the community that they wanted to teach kids courtesy and being polite, and since other martial arts are expensive, with a lot of equipment, they decided a sumo dohyo was the best option." Euan McKirdy/CNN
Yuki and Masato's father, who declined to give his name, alludes to the notion of "yamato damashi," the quasi-militaristic perception of "Japaneseness."
"Traditional sports like sumo are something that makes a Japanese person" he says. "There is a fact that yamato damashi is lacking these days but it's also that something that we originally had is being forgotten.
"It's important through sumo and other traditional sports that we can bring back something that we've forgotten inside as Japanese. It's something that we want (the coaches) to pass on to the next generation." Euan McKirdy/CNN